[accordion_father active=”0″][accordion_son size=”24″ title=”Basic Cancer Information”]Cancer is the uncontrolled growth of abnormal cells in the body. Cancer develops when the body’s normal control mechanism stops working. Old cells do not die and cells grow out of control, forming new, abnormal cells. These extra cells may form a mass of tissue, called a tumour. Some cancers, such as leukaemia, do not form tumours.[/accordion_son][accordion_son size=”24″ title=”A Collection of Related Diseases”]Cancer is the name given to a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues.

Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and divide to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place.

When cancer develops, however, this orderly process breaks down. As cells become more and more abnormal, old or damaged cells survive when they should die, and new cells form when they are not needed. These extra cells can divide without stopping and may form growths called tumours.

Many cancers form solid tumours, which are masses of tissue. Cancers of the blood, such as leukaemias, generally do not form solid tumours.

Cancerous tumours are malignant, which means they can spread into, or invade nearby tissues. In addition, as these tumours grow, some cancer cells can break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumour.

Unlike malignant tumours, benign tumours do not spread into, or invade nearby tissues. Benign tumours can sometimes be quite large, however. When removed, they usually don’t grow back, whereas malignant tumours sometimes do. Unlike most benign tumours elsewhere in the body, benign brain tumours can be life-threatening.[/accordion_son][accordion_son size=”24″ title=”What are the most common forms of cancer?”]Cancer can occur anywhere in the body. In women, breast cancer is most common. In men, it’s prostate cancer. Lung cancer and colorectal cancer affect both men and women in high numbers.

There are five main categories of cancer:

  • Carcinomas begin in the skin or tissues that line the internal organs.
  • Sarcomas develop in the bone, cartilage, fat, muscle or other connective tissues.
  • Leukaemia begins in the blood and bone marrow.
  • Lymphomas start in the immune system.
  • Central nervous system cancers develop in the brain and spinal cord.

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CELL DIFFERENCES

Cancer cells differ from normal cells in many ways that allow them to grow out of control and become invasive. One important difference is that cancer cells are less specialized than normal cells. That is, whereas normal cells mature into very distinct cell types with specific functions, cancer cells do not. This is one reason that, unlike normal cells, cancer cells continue to divide without stopping.

In addition, cancer cells are able to ignore signals that normally tell cells to stop dividing or that begin a process known as programmed cell death, or apoptosis, which the body uses to get rid of unneeded cells.

Cancer cells may be able to influence the normal cells, molecules, and blood vessels that surround and feed a tumorous area known as the microenvironment. For instance, cancer cells can induce nearby normal cells to form blood vessels that supply tumours with oxygen and nutrients, which they need to grow. These blood vessels also remove waste products from tumours.

Cancer cells are also often able to evade the immune system, a network of organs, tissues, and specialized cells that protects the body from infections and other conditions. Although the immune system normally removes damaged or abnormal cells from the body, some cancer cells are able to hide from the immune system.

Tumors can also use the immune system to stay alive and grow. For example, with the help of certain immune system cells that normally prevent a runaway immune response, cancer cells can actually keep the immune system from killing cancer cells.

HOW CANCER ARISES AND DRIVERS

[accordion_father active=”0″][accordion_son size=”24″ title=”How Cancer Arises”]Cancer is a genetic disease, that is, it is caused by changes to genes that control the way our cells function, especially how they grow and divide.

Genetic changes that cause cancer can be inherited from our parents. They can also arise during a person’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun.

Each person’s cancer has a unique combination of genetic changes. As cancer continues to grow, additional changes will occur. Even within the same tumour, different cells may have different genetic changes.

In general, cancer cells have more genetic changes, such as mutations in DNA, than normal cells. Some of these changes may have nothing to do with cancer; they may be the result of cancer, rather than its cause.[/accordion_son][accordion_son size=”24″ title=”“Drivers“ of Cancer”]The genetic changes that contribute to cancer tend to affect three main types of genes, proto-oncogenes, tumour suppressor genes, and DNA repair genes. These changes are sometimes called drivers of cancer.

Proto-oncogenes are involved in normal cell growth and division. However, when these genes are altered in certain ways or are more active than normal, they may become cancer-causing genes (or oncogenes), allowing cells to grow and survive when they should not.

Tumour suppressor genes are also involved in controlling cell growth and division. Cells with certain alterations in tumour suppressor genes may divide in an uncontrolled manner.

DNA repair genes are involved in fixing damaged DNA. Cells with mutations in these genes tend to develop additional mutations in other genes. Together, these mutations may cause the cells to become cancerous.

As scientists have learned more about the molecular changes that lead to cancer, they have found that certain mutations commonly occur in many types of cancer. Because of this, cancers are sometimes characterized by the types of genetic alterations that are believed to be driving them, not just by where they develop in the body and how the cancer cells look under the microscope.[/accordion_son][/accordion_father]

WHEN CANCER SPREADS

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In metastasis, cancer cells break away from where they first formed (primary cancer), travel through the blood or lymph system, and form new tumours (metastatic tumours) in other parts of the body. The metastatic tumour is the same type of cancer as the primary tumour.

Cancer that has spread from the place where it first started to another place in the body is called metastatic cancer. The process by which cancer cells spread to other parts of the body is called metastasis.

TISSUE CHANGES THAT ARE NOT CANCER

Not every change in the body’s tissues is cancer. Some tissue changes may develop into cancer if they are not treated, however. Here are some examples of tissue changes that are not cancer but, in some cases, are monitored:

Hyperplasia occurs when cells within a tissue divide faster than normal and extra cells build up or proliferate. However, the cells and the way the tissue is organized look normal under a microscope. Hyperplasia can be caused by several factors or conditions, including chronic irritation.

Dysplasia is a more serious condition than hyperplasia. In dysplasia, there is also a buildup of extra cells. But the cells look abnormal and there are changes in how the tissue is organized. In general, the more abnormal the cells and tissue look, the greater the chance that cancer will form.

Some types of dysplasia may need to be monitored or treated. An example of dysplasia is an abnormal mole (called a dysplastic nevus) that forms on the skin. A dysplastic nevus can turn into melanoma, although most do not.

An even more serious condition is carcinoma in situ. Although it is sometimes called cancer, carcinoma in situ is not cancer because the abnormal cells do not spread beyond the original tissue. That is, they do not invade nearby tissue the way that cancer cells do. But, because some carcinomas in situ may become cancer, they are usually treated.

 

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Normal cells may become cancer cells. Before cancer cells form in tissues of the body, the cells go through abnormal changes called hyperplasia and dysplasia. In hyperplasia, there is an increase in the number of cells in an organ or tissue that appear normal under a microscope. In dysplasia, the cells look abnormal under a microscope but are not cancer. Hyperplasia and dysplasia may or may not become cancer.

Credit: Terese Winslow LLC

TYPES OF CANCER

There are more than 100 types of cancer. Types of cancer are usually named for the organs or tissues where the cancers form. For example, lung cancer starts in cells of the lung, and brain cancer starts in cells of the brain. Cancers also may be described by the type of cell that formed them, such as an epithelial cell or a squamous cell.

Here are some categories of cancers that begin in specific types of cells:

 

Carcinoma

Carcinomas are the most common type of cancer. They are formed by epithelial cells, which are the cells that cover the inside and outside surfaces of the body. There are many types of epithelial cells, which often have a column-like shape when viewed under a microscope.

Cancers under this category include cancers of the breast, colon, prostate, bladder, ureters, kidneys

Soft tissue sarcoma forms in soft tissues of the body, including muscle, tendons, fat, blood vessels, lymph vessels, nerves, and tissue around joints.

Sarcomas are cancers that form in bone and soft tissues, including muscle, fat, blood vessels, lymph vessels, and fibrous tissue (such as tendons and ligaments).

Osteosarcoma is the most common cancer of the bone. The most common types of soft tissue sarcoma are leiomyosarcoma, Kaposi sarcoma, malignant fibrous histiocytoma, liposarcoma, and dermatofibrosarcoma protuberans.

Leukemia

Cancers that begin in the blood-forming tissue of the bone marrow are called leukaemias. These cancers do not form solid tumours. Instead, large numbers of abnormal white blood cells (leukaemia cells and leukemic blast cells) build up in the blood and bone marrow, crowding out normal blood cells. The low level of normal blood cells can make it harder for the body to get oxygen to its tissues, control bleeding, or fight infections.

There are four common types of leukaemia, which are grouped based on how quickly the disease gets worse (acute or chronic) and on the type of blood cell cancer starts in (lymphoblastic or myeloid).

Lymphoma

Lymphoma is cancer that begins in lymphocytes (T cells or B cells). These are disease-fighting white blood cells that are part of the immune system. In lymphoma, abnormal lymphocytes build up in lymph nodes and lymph vessels, as well as in other organs of the body.

There are two main types of lymphoma:

Hodgkin lymphoma – People with this disease have abnormal lymphocytes that are called Reed-Sternberg cells. These cells usually form from B cells.

Non-Hodgkin lymphoma – This is a large group of cancers that start in lymphocytes. The cancers can grow quickly or slowly and can form from B cells or T cells.

Multiple Myeloma

Multiple myelomas is cancer that begins in plasma cells, another type of immune cell. The abnormal plasma cells, called myeloma cells, build up in the bone marrow and form tumours in bones all through the body. Multiple myelomas is also called plasma cell myeloma and Kahler disease.

Melanoma

Melanoma is cancer that begins in cells that become melanocytes, which are specialized cells that make melanin (the pigment that gives skin its colour). Most melanomas form on the skin, but melanomas can also form in other pigmented tissues, such as the eye.

Brain and Spinal Cord Tumours

There are different types of brain and spinal cord tumours. These tumours are named based on the type of cell in which they formed and where the tumour first formed in the central nervous system. For example, an astrocytic tumour begins in star-shaped brain cells called astrocytes, which help keep nerve cells healthy. Brain tumours can be benign (not cancer) or malignant (cancer).

Credit: National Cancer Institute